A reference voltage generation circuit generates a reference voltage corresponding to a desired temperature characteristic. As the reference voltage generation circuit, a band gap reference circuit is generally known. The band gap reference circuit (hereafter BGR circuit) generates a constant voltage against a temperature change by adding a voltage having a positive temperature characteristic to a voltage having a negative temperature characteristic. The BGR circuit is described in patent document, International Publication WO 2008/120350, for example.
On the other hand, in regard to an oscillation circuit, there is known an RC oscillation circuit including inverters of odd-numbered stages and an R, C circuit disposed on an inverter output node, as described in patent document, Japanese Laid-open Patent Publication No. 2008-252414, for example. As a clock source provided internally in an LSI, it is generally configured of an external crystal oscillator and a frequency division circuit which is disposed internally in the LSI for frequency dividing highly accurate clocks generated by the crystal oscillator. Further, as a technique without using a crystal oscillator, it has been proposed to form an oscillation circuit internally in an LSI, so as to be used for an internal clock source.
A power regulator generates and supplies internal power to the oscillation circuit incorporated in the LSI, based on a reference voltage generated by a reference voltage generation circuit such as a BGR circuit. In general, an internal power supply provides a constant voltage without temperature dependence. Therefore, the reference voltage generation circuit outputs a constant voltage without temperature dependence as the reference voltage.
To an LSI of recent years, various kinds of specifications are desired. For example, corresponding to the fast operation of a transistor incorporated in the LSI at a high temperature, there is wanted fast processing by raising the frequency of the oscillation circuit, or oppositely, suppression of increased power consumption which accompanies fast operation of the incorporated transistor at a high temperature, by decreasing the frequency of the oscillation circuit.